1. Field of the Invention
The present invention relates to a filter for removing noise, and more particularly, to a filter for removing noise that is capable of improving performance by increasing magnetic permeability and improving impedance characteristics through simple structure and process.
2. Description of the Related Art
Electronic products, such as digital TVs, smart phones, and notebook computers, have functions for data communication in radio-frequency bands. Such IT electronic products are expected to be more widely used since they have multifunctional and complex features by connecting not only one device but also USBs and other communication ports.
Here, for higher-speed data communication, data are communicated through more internal signal lines by moving from MHz frequency bands to GHz radio-frequency bands.
When more data are communicated between a main device and a peripheral device over a GHz radio-frequency band, it is difficult to provide smooth data processing due to signal delay and other noises.
Therefore, there is a need for immunity measures for preventing malfunctions due to external noises as well as preventing electronic products themselves from being noise sources.
In order to solve the above problem, an EMI prevention part is provided around the connection between an IT device and a peripheral device. However, conventional EMI prevention parts are used only in limited regions such as specific portions and large-area substrates since they are coil-type and stack-type and have large chip part sizes and poor electrical characteristics. Therefore, there is a need for EMI prevention parts that are suitable for slim, miniaturized, complex, and multifunctional features of electronic products.
A common-mode filter of EMI prevention coil parts in accordance with the prior art is described below in detail with reference to FIGS. 1.
Referring to FIG. 1, a conventional common-mode filter includes a lower magnetic substrate 10, an insulating layer 20 disposed on the lower magnetic substrate 10 and including a first coil pattern 21 and a second coil pattern 22 which are vertically symmetrical to each other, and an upper magnetic substrate 30 disposed on the insulating layer 20.
Here, although not shown in detail, the insulating layer 20 may be configured by coupling a sheet-type first insulating layer including the first coil pattern and a sheet-type second insulating layer including the second coil pattern in a stack type.
And, although not shown in detail, a first input lead pattern and a first output lead pattern for inputting and outputting electricity to and from the first coil pattern 21 may be formed on the insulating layer 20. A second input lead pattern and a second output lead pattern for inputting and outputting electricity to and from the second coil pattern 22 may be formed on the insulating layer 20.
At this time, the insulating layer 20 may be configured by coupling a sheet-type third insulating layer including the first and second output lead patterns with the second insulating layer in a stack type.
Further, the first coil pattern 21 and the second coil pattern 22 may be electrically connected to the first output lead pattern and the second output lead pattern through via connection structures, respectively.
Meanwhile, the upper magnetic substrate 30 and the lower magnetic substrate 10 are respectively manufactured in the form of a substrate by sintering ferrite powder of the same composition to be matched with each other and bonded to upper and lower surfaces of the insulating layer 20 including the first coil pattern 21 and the second coil pattern 22.
However, in order to implement an impedance characteristic value, the most important characteristics of the conventional common-mode filter configured as above, approximate to design values, the compositions of the upper magnetic substrate 30 and the lower magnetic substrate 10 should be uniformly mixed, but since differences in particle growth according to sintering and curing behaviors occur according to particle sizes during actual sintering, there occur phenomena such as a decrease in magnetic permeability, which locally exerts a bad effect on the impedance characteristics.
In this case, noise removal characteristics are remarkably deteriorated since it is difficult to smoothly perform removal of signal delay and noise signals due to a decrease in impedance in GHz radio-frequency bands.
Especially, the compositions of the upper magnetic substrate 30 and the lower magnetic substrate are manufactured by mixing a polymer resin in ferrite powder to increase adhesion with the insulating layer 20. In this case, although the adhesion is increased, magnetic permeability, that is, magnetic characteristics to design values of the common-mode filter is remarkably reduced due to non-uniformity of particle dispersion and mixing of the ferrite powder and the polymer resin, difficulty in rearrangement of particles according to the sintering and curing behaviors, and magnetic permeability due to the resin component during sintering. Therefore, the noise removal performance and characteristics of the product are deteriorated due to changes in resonance frequency and parasitic capacitance.
When a particle size of the ferrite constituting the upper magnetic body 30 is increased to increase permeability, radio-frequency characteristics of the common-mode filter are deteriorated, and when the amount of the resin as a binder of the upper magnetic body 30 is reduced, the adhesion, insulation, and withstand voltage characteristics of the upper magnetic body 30 are deteriorated.
Further, in order to increase permeability, there is a method of providing a high-temperature environment when forming the upper magnetic body 30, but there are problems such as deterioration of workability, increase of equipment for increasing a temperature, and deterioration of reliability of the common-mode filter in the high-temperature environment.